Modern mass rapid transit rail systems are very effective carriers of people. They are generally grade separated systems to enable vehicles to operate unaffected by automobile traffic, and thereby are able to achieve traffic densities otherwise unachievable. They are, however, very expensive. A typical, but conservative order of magnitude system capital cost for a system is approximately $100 million per bi-directional track mile of system, making it difficult for communities and cities to justify and/or afford the cost of new construction. This limitation has the effect of constraining the reach of these systems, and thus limiting the convenience to the users who can only ride the systems to the few locations to which guideway has been constructed. This results in a classic case of Catch 22. The high cost of systems requires a high ridership to justify the cost. However, high guideway costs limit construction and thus the reach of fixed guideway systems. This limits convenience to the riders, making it difficult to achieve the high ridership needed to justify the high cost.
Conventional mass rapid transit rail technology attempts to improve the benefits per cost by focusing on serving the commuting public. This means building systems to achieve very high passenger capacities to major employment centers. An example conventional system is shown in FIG. 1. As shown, conventional systems 110 achieve high capacities by building heavy infrastructure and operating long heavy trains 112 that typically carry a large number of riders to the few large employment centers that they can most effectively service, while bypassing smaller towns or communities. This, however, requires very costly guideway 122 and station structures 124, which limits the system's reach and thus convenience for the users, especially for those who want to travel to the generally more widely distributed retail, residential, or recreational destinations.
With guideway 122 and station structures 124 that must be built to handle long heavy trains 112 to support demand during commute hours, the result is an expensive but marginally justifiable solution for commute hour travel which is far too expensive to justify for other periods of the day and other destinations.
Other existing transportation systems that aim to be less expensive to build and operate include automated people mover (APM) systems, such as those operating in many modern airports and some cities. These systems are low speed/low capacity systems that operate driverless vehicles at speeds in the range of 25 to 30 mph and achieve line capacities in the range of 2,000 to 3,000 passengers per hour per direction. Given the limited speed and capacity of these systems, even with the somewhat lower cost of construction due to the use of smaller vehicles, the benefit/cost is still poor. Furthermore, with the lower speeds and line capacities, these systems are limited in utility to local service routes.
Another type of transportation system that has been discussed is called “personal rapid transit” (PRT). PRT's differ from the more common APM systems in that these systems are built with offline stations which allow higher traffic densities to be achieved. Typically these systems operate driverless cars that seat four to six people and can provide service on a personal demand-driven basis. However, with the very small cars, high speeds are difficult to achieve and line capacities are severely restricted. There is one PRT that is operating at West Virginia University, the Morgantown PRT, which is an 8.2 mile long system having cars that seat 20 people. With a claim of 15 second headways a line capacity of 4,800 passengers per hour per direction can be achieved. With rubber-tired vehicles, however, the top speed of the system is 30 mph thus limiting its applicability to low speed local service lines.
Although the above examples are, sometimes considered “modern era” technologies, a more traditional but yet still widely deployed form of rail transit is conventional light rail transit (LRT). These systems operate rail cars at street level and thus intermingled with automobile traffic. The rail vehicles are not driverless and traffic density is severely limited due in large part by the fact that street inter-sections must be kept unobstructed for a significant percentage of time to allow for automobile traffic to cross. Given the dangers of operating in mixed traffic with cars and pedestrians, LRT systems typically limit their speeds to under 30 mph. Furthermore, although cars can be operated in consists of 2 to 4 cars, longer consists are impractical in mixed traffic, which then limits line capacities to about 4,000 passengers per hour per direction. Again, with the low speeds and low capacity, the LRT technology has not shown itself to be practical for anything more than local service lines.